Imaging apparatus include devices that are configured to selectively produce predefined images on one or more types of imaging media. Examples of images produces by imaging apparatus include letters and other documents, as well as graphical images such as photographs and the like. Among the various types of imaging apparatus that are presently available, the type generally known as the “inkjet printer” is one of the more popular. Although the general operation and function of inkjet printers is well known in the art, a brief overview is provided herein.
The operation of a typical inkjet printer involves advancing, or moving, a sheet of paper (or other imaging media) vertically (typically) relative to a print nozzle from which tiny droplets of ink are precisely and accurately projected, or “fired,” onto the paper in order to produce the desired image. The print nozzle is also typically independently movable in transverse relation to the direction of advancement of the imaging media. Thus, the advancement of the paper, along with the transverse movement relative thereto of the print nozzle, effectively provides the print nozzle with a two-dimensional range of movement relative to the sheet of paper upon which the image is to be printed.
Typical inkjet printers include one or more ink cartridges, each having at least one reservoir chamber in which ink is stored for use. The reservoir chamber is generally defined, or enclosed, by a multifaceted, enclosed wall that is usually fabricated from rigid plastic or the like. The print nozzle, or nozzle assembly, which is mentioned above, is also included with each ink cartridge. The nozzle assembly is usually supported on the exterior of the wall which defines the reservoir chamber. Ink from the reservoir chamber is directly supplied to the nozzle assembly through an opening in the wall.
The nozzle assembly generally defines one or more capillary passages into which ink from the chamber is allowed to flow. More specifically, each capillary passage has two opposite termini, wherein one of the termini is fluidly communicable with the reservoir chamber and the other termini is precisely oriented so as to be directed, or aimed, at the imaging media.
In many applications the nozzle assembly generally also includes a selectively controlled heater associated with at least one capillary passage. Each heater is typically in the form of a selectively controlled electrical resistor, or the like, that is capable of providing a nearly instantaneous and substantial increase in temperature, thereby vaporizing a portion of the ink within the associated capillary passage.
The vaporization of the ink within the capillary passage causes the formation of a rapidly expanding “bubble” of ink vapor within the capillary passage which, in turn, causes a droplet of ink to be projected out of the capillary passage and toward the sheet of paper. The vapor “bubble” quickly contracts by cooling, and/or escapes from the capillary passage, whereupon the capillary passage is replenished with liquid ink is drawn into the capillary passage from the reservoir chamber by way of capillary attraction.
A well-known practice within the art is to employ a type of foam material within the reservoir chamber to control the flow of ink out of the chamber and to control the flow of air into the chamber. For example, it is known that such employment of foam material can prevent the unintended leakage, or “drooling,” of ink out of the nozzle. A common type of foam material thus employed is that of open cell urethane foam.
The foam functions to control ink flow by way of capillary attraction. That is, the cells and passages within the foam material are generally of a size that will cause ink to be drawn into the foam material by way of capillary attraction. One example of a foam-type ink reservoir system is described in U.S. Pat. No. 5,509,140, which is hereby incorporated herein by reference in its entirety.
Thus, a typical inkjet cartridge contains a given quantity of foam material in which a given volume of ink can be “entrained,” or absorbed by way of capillary attraction. Generally, the foam material is located substantially adjacent to the nozzle assembly so that ink is drawn directly to the nozzle assembly from the foam, although in most cases, a small open chamber called a “standpipe area” is employed between the foam and the nozzle assembly. Thus, typically, the ink is drawn into the standpipe area from the foam and then is drawn from the standpipe area in to the nozzle assembly for firing.
One specific type of prior art ink cartridge configuration consists of a single reservoir chamber that is substantially filled with foam in which ink can be entrained. In such a configuration, substantially the entire quantity of ink available for printing is entrained within the foam material. However, another prior art ink cartridge configuration has both a free ink chamber and an entrained ink chamber that are substantially separated from one another by a dividing barrier that is usually incorporated into the wall that is described above.
In such a two-chamber configuration, both the entrained ink chamber and the free ink chamber are generally rectilinear, and the barrier separating them is generally in the form of a substantially flat, rigid panel. A port, or hole, is usually defined near the bottom of the panel, whereby ink can migrate between the free ink chamber and the entrained ink chamber. The entrained ink chamber of such a two-chamber configuration is generally substantially filled with a quantity of foam material, while the free ink portion is generally simply an open chamber in which a quantity of free-flowing ink can be contained.
In either of the prior art inkjet cartridge configurations discussed above, the capillary attraction of the ink into the foam material generally at least partially counteracts the head pressure of the ink with respect to the nozzle assembly. That is, the capillary characteristics of the foam material in addition to the capillary characteristics of the capillary passage of the nozzle assembly generally overcome the head pressure of the ink within the chamber.
This counteractive characteristic provided by the capillary attraction of the foam material is generally referred to as “back pressure” and tends to prevent the ink from leaking or drooling out of the nozzle assembly until the ink is fired by way of the heater as explained above. The capillary characteristics of the foam material provide other benefits in connection with the function of a typical ink cartridge as is explained below.
The typical ink cartridge, whether a one-chamber or a two-chamber configuration, also generally includes a vent system that allows air to enter the ink cartridge to displace ink that is removed from the cartridge because of the printing process. Generally, a typical vent system includes a vent opening that is defined in the cartridge, preferably near the top of the entrained ink chamber, wherein the vent opening is fluidly communicable with the ambient atmosphere.
In the two-chamber type of ink cartridges that consist of both an entrained ink portion and a free ink portion, the foam material is located in the entrained ink chamber between the vent opening and the port which leads to the free ink chamber, so that air entering the cartridge by way of the vent opening must travel past the foam material before entering the free ink portion of the chamber. That is, the ink in the free ink chamber is generally sealed from ambient pressure by way of the foam material and the ink entrained therein. Additionally, the foam is substantially adjacent to the nozzle assembly, or the standpipe area, as explained above.
As the ink is consumed from the ink cartridge as the result of the printing process, the ink is drawn into the nozzle assembly from the foam material as mentioned above. This, in turn, causes free ink to flow from the free ink chamber of the cartridge and into the foam of the entrained ink chamber by way of the port. This flow of free ink into the foam material is aided both by the head pressure of the ink in the free ink chamber and by the capillary attraction of the foam material.
However, as ink is drawn from the free ink chamber, the level of the ink therein falls which results in a decrease in head pressure. Additionally, as the ink level within the free ink chamber falls as it is drawn therefrom, a partial vacuum develops in the free ink chamber above the volume of free ink. This buildup of the partial vacuum in the free ink chamber above the free ink tends to further impede the flow of ink out of the free ink chamber.
Consequently, as the level of free ink falls in the free ink chamber, the level of ink entrained within the foam material in the entrained ink chamber correspondingly falls because the capillary attraction of the foam material is resisted by the vacuum formed in the free ink chamber. As the level of entrained ink continues to fall along with a continued vacuum build up above the free ink, a point is reached at which atmospheric air at ambient pressure overcomes the seal provided by the foam material and the ink entrained therein, whereupon a quantity of atmospheric air forces its way past the foam and entrained ink, thereby entering into the free ink chamber by way of the port.
The entrance of atmospheric air into the free ink chamber in this manner at least partially relieves the vacuum buildup therein and above the free ink, thus increasing the effective head pressure of the free ink with respect to the foam material. As a result of the entrance of the air into the free ink chamber as explained above, ink migrates more freely from free ink chamber and into the entrained ink chamber, causing the level of entrained ink in the entrained ink chamber to rise. The rising level of ink in the entrained ink chamber again creates a seal against atmospheric air which, in turn, allows a partial vacuum to again begin building up in the free ink chamber. This “self-regulating” cycle continues until substantially all of the ink is used up from the cartridge.
As mentioned briefly above, prior art two-chamber ink cartridges generally include an interior dividing barrier in the form of a flat panel wall that separates the entrained ink chamber from the free ink chamber. That is, prior art two-chamber ink cartridges generally include two distinct side-by-side chambers, wherein one chamber is substantially filled with foam material and the other chamber is devoid of foam material.
The port defined in the wall is generally in the form of an orifice or a passage through which ink flows from the open free ink chamber into the foam-filled entrained ink chamber. Likewise, air flows in the opposite direction, from the entrained ink chamber to the free ink chamber, during the self-regulating pressure equalization process which is described above. Additionally, as mentioned above, the vent opening and the nozzle assembly are generally fluidly communicable with the foam-filled entrained ink chamber, while being substantially sealed from the free ink chamber by the foam material.
A feature that is generally common to most, if not all, two-chamber prior art ink cartridges is that the foam-filled entrained ink chamber is substantially dimensionally and volumetrically comparable to the open free ink chamber. In other words, it is not uncommon for a prior art ink cartridge to have a foam-filled entrained ink chamber that is at least fifty percent as large as the open free ink chamber. This aspect of the prior art is generally undesirable in that such relatively large quantities of foam material displace equally large volumes of ink. That is, the foam material of prior art ink cartridges displaces a significant quantity of ink notwithstanding the capability of the foam material to “absorb” a given quantity of ink.
Thus, while prior art ink cartridges are known to function satisfactorily, the volumetric efficiency of the typical prior art ink cartridge is poor. That is, a substantial portion of the ink storage capacity of a typical prior art ink cartridge is devoted to housing a relatively large quantity of foam material that displaces an equal volume of ink which could otherwise be stored in the cartridge. In other words, prior art ink cartridges could typically store a significantly greater volume of ink if not for ink otherwise displaced by the foam material. Therefore, an increase in the volumetric efficiency of prior art ink cartridges is desirable.
What is needed then is an inkjet cartridge that achieves the benefits to be derived from similar prior art devices, but which avoids the shortcomings and detriments individually associated therewith.